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//数值 toFixed（参数） 参数代表保留几位小数
let pi =3.1415926;
 console.log(pi .toFixed(2)); 
 //Math.pow(n,m)n代表计算的底数，m代表幂
 console.log(Math.pow(2,3));
 console.log(Math.pow(2,53));
 //判断NaN
 console.log( isNaN(2));//false
 console.log( NaN === NaN);

 //parseInt()转换 为正整数 从左往右依次开始，遇到非数字停下
 let num = '123456afg'
 console.log(parseInt(num));
 console.log(parseInt(0x100));
 console.log(16*16);
 //parseFloat()；转换为浮点数，从左往右依次看ii是

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